The present invention relates generally to systems and methods for accurately measuring pressure, and more particularly, to a system and method for improving the performance of a pressure measuring device by regulating its temperature.
Pressure sensors are used extensively throughout the semiconductor industry in fabrication processes in order to control the flow of process gases to process chambers. In particular, variable capacitance manometers can be utilized to measure and regulate the pressure of these gasses. The sensing element within a variable capacitance manometer is a diaphragm which is deflected by the pressure of process gases. Closely positioned near the diaphragm is a fixed electrode, forming a capacitor which translates deflections in the diaphragm into a change in capacitance reflective of the pressure of the process gas.
When used in fabrication processes, the sensor is exposed to the flow of process gases. Often, these gases become contaminated during the fabrication process, and may in turn contaminate the diaphragm of the variable capacitance manometer. The process gases may also condense upon the diaphragm and subsequently react with the material of the diaphragm to form a layer of undesired material. Because the function and accuracy of the manometer is based upon deflection of the diaphragm, the weight and thickness added to the diaphragm from these process-related by-products can impair the accuracy of the variable capacitance manometer. Ultimately, this layer of by-products may swell to such proportions that the difference capacitance manometer ceases functioning altogether.
To prevent the formation of this unwelcome layer of by-products, the variable capacitance manometer can be operated at an elevated temperature, typically slightly above the process temperature. In the vast majority of cases, elevation of the sensor""s temperature is accomplished through the use of an oven. This oven is typically a structure which surrounds the variable capacitance sensor and regulates its temperature.
Heating the variable capacitance sensor using these conventional ovens, however, comes replete with its own set of pitfalls. The accuracy of the sensor is dependent upon the uniformity and the consistency of the temperature within the sensor, but the evenness of temperature within the sensor is often affected by heat loss through, for example, the vacuum fitting coupling the sensor to the remainder of the process gas flow system. Since this structure protrudes from the oven and is exposed to external influences it is typically cooler than the remainder of the sensor. Because this is usually where the most heat loss occurs, in most designs the sensor is heated at the point where the sensor is vacuum fitted to the remainder of the process gas flow system. In other areas, the sensor is heated indirectly through an airspace. While this indirect heating does tend to reduce temperature gradients in the sensor""s structure, it typically results in an over-sized oven with a large air-space between the sensor and oven walls and, in general, a large and inefficient package.
Another approach, elimination of the oven airspace by utilizing simple, direct heating of the sensors results in a more compact, energy efficient design which reaches a set point more quickly. Unfortunately, these existing directly heated designs suffer dramatically from the effects of temperature gradients and perturbations within their structures.
Ultimately, there is a need for a system and method that has the improved accuracy and other advantages of an oven heated pressure sensor with neither the size of an indirect heating unit nor the effects of temperature gradients created in a directly heated temperature sensor.
The present invention provides a temperature regulating system and method, the various embodiments of which substantially eliminate or reduce the disadvantages and problems associated with previously developed systems and methods.
More specifically, one embodiment of the present invention provides a system and method of heating the pressure sensing element of a pressure sensing device such as a variable capacitance manometer, and minimizing the temperature gradients within the sensor""s structure. The temperature regulating system and method include a temperature regulating device that surrounds a pressure sensor and can convey heat to select zones of the sensor. A temperature sensor monitors these zones and the temperature in one or more of these zones is adjusted based upon the measured temperature differential between the zones.
In one embodiment, the present invention provides the ability to more accurately measure temperature gradients and adherence to a set point by utilizing an ambient temperature measurement device in combination with a measurement of the temperature differential between the temperature regulated zones.
One embodiment of the present invention offers an important technical advantage by providing a more direct and compact means of heating the pressure sensing element of a variable capacitance manometer.
One embodiment of the present invention offers another technical advantage by reducing the amount of insulation between the temperature regulator and the pressure sensor.
One embodiment of the present invention offers yet another technical advantage by reducing the amount of energy consumed in regulating the temperature of the sensor.
One embodiment of the present invention offers a further technical advantage by reducing the amount of time that is required for the pressure sensor to reach a set point temperature.